A network address translator (NAT) is a device that can translate Internet Protocol (IP) addresses and TCP/UDP port numbers of data packets as the packets are forwarded. For example, a small business network with multiple computers that connect to the Internet may employ an NAT for such connections. This type business would normally have to obtain a public IP address for each computer on the network from an Internet service provider (ISP). With the NAT, however, the small business can use private addressing and have the NAT map its private addresses to single or to multiple public IP addresses. The NAT is a common solution for the following combination of requirements: leveraging the use of a single connection, rather than connecting multiple computers, to the Internet; using private addressing; and providing access to Internet resources without having to deploy a proxy server. Also, these translators provide a type of firewall protection by hiding internal IP addresses and they enable companies to employ more internal IP addresses since there is no possibility of conflict with addresses outside the companies' private domain.
One major obstacle in NAT technology is that there is a plurality of differing protocols that may be employed for translating network traffic. For instance, many consumer or home systems utilize Cone, Full Cone, or Restricted Cone NAT technologies whereby some routers may behave as a Cone NAT for UDP traffic and behave as a symmetric NAT for TCP traffic. In corporate situations, symmetric NAT along with hardware or software firewalls are more likely to be employed. Currently, in order to communicate over the differing types of protocols, intense manual configurations are required to properly configure the NAT to communicate over one of the above mentioned protocols. However, many network situations may require more than one protocol to be employed in order for communications to occur between remote applications.
Other problems occur as hosts move from one network to another, wherein the hosts may rely on the local network to assign their network address. This address may be a complete routable address on the Internet, or it may be an un-routable address that is behind a Network Address Translation (NAT) system. These hosts have what is commonly known as a Dynamic IP addresses or a NAT'ed IP address. Devices with a NAT'ed IP address generally do not have the ability to accept incoming TCP connections for services unless they have some method of registering a port to be remapped by the NAT system for that specific host service. It is generally not possible for another host on the Internet to discover this assigned address or mapped port for that service using normal address discovery means such as a Domain Name System (DNS) or service. While some services exist to solve Dynamic IP problems (Dynamic DNS), they generally do not function with caching DNS servers and also they generally cannot resolve dynamic port numbers.